There is a certain class of radars that feature a transmitter (and associated equipments) separated from, but connected to, the antenna. With increased emphasis being placed on the costs of such equipment, it has become common to use commercial off-the-shelf (COTS) equipment wherever possible. Consequently, the radar transmitter may be built using COTS. However, COTS equipment is generally more fragile than militarized equipment, and may be subject to failure in severe environments. For protection against severe acceleration or vibration, COTS-equipped transmitters may be mounted on a mechanical isolation system, which attenuates severe acceleration by transforming accelerations into large deflections. As a result, significant motion can be expected between the transmitter and the associated antenna, which must be accommodated.
In a radar context, relatively large amounts of radio-frequency (RF) energy are involved, and low losses are desirable. Such requirements suggest the use of “transmission lines,” which are conductor arrangements which exhibit controlled surge resistance or “characteristic impedance.” Most often, the characteristic impedance remains constant throughout the length of the transmission line, but transmission lines with varying impedance are known. One of the types of transmission line often used with radar systems is “waveguide,” of which many forms are known, including “circular” and “rectangular.” A circular or rectangular waveguide takes the form of a hollow tube of electrically conductive material having a circular or rectangular cross-sectional shape. Such waveguides may be “rigid” (self-supporting), typically made from thick-wall aluminum, or “flexible,” typically made from corrugated thin-wall copper-alloy material. In this context, “flexible” means that the waveguide deforms significantly under its own weight. The flexible waveguides are sometimes known as “flexguide.”
FIG. 1a illustrates a mechanical system 10 including an antenna illustrated as a block 12 with a radiating face 12rf, a transmitter (TX) illustrated as a block 14, and a flexible rectangular waveguide 16 extending therebetween. Waveguide 16 is fastened to a flange 14f, which in turn is fastened to a mating location on antenna 12. A similar flange (not visible in FIG. 1a) fastens the other end of waveguide 16 to a mating portion of transmitter block 14. In this context, it should be understood that the term “between” is used in its electrical sense, rather than in its mechanical or location sense. FIG. 1b illustrates the same structure as that of FIG. 1a, but shows the flexible waveguide 26 as extending between blocks 12 and 14 and making attachment by a flange 26f to block 14, but not lying physically between the blocks 12 and 14. In its electrical sense, the term “between” means that there is an electrical energy transmission path (or signals are coupled) from one of the blocks to the other, and possibly bidirectionally.
The purpose of the waveguide is to provide an electrically stable energy transmission path from the transmitter to the antenna. The reason for using flexible waveguide in FIGS. 1a and 1b rather than rigid waveguide is to accommodate or “take up” the relative motion between the transmitter and the antenna. Ideally, the waveguide would exhibit constant loading-to-stiffness ratio along its length. When a length of flexible waveguide extends between objects in relative motion, such as the transmitter and antenna of FIGS. 1a and 1b, a simplistic assumption is that the waveguide will flex uniformly along its length, thereby distributing the bending or deformation associated with the motion. Unfortunately, slight variations in manufacture of the waveguide will result in greater rigidity of some portions of the guide than at other portions. Consequently, bending will take place preferentially at certain locations. Thus, the bending associated with the relative motion, rather than being distributed uniformly along the length of the transmission line, tends to occur at specific locations, and may have deleterious electrical effects at such locations, such as electrical phase and impedance changes. Also, it is well known that repeated flexing or bending of a metallic object at a particular location tends to work harden or crystallize the metal, and ultimately results in cracks and failure. This form of failure is known as “fatigue failure.” Fatigue failure is exacerbated if the waveguide structure is resonant in a range of frequencies which includes the input excitation frequency, because the amount of motion becomes amplified with respect to the applied excitation. It is difficult to design a waveguide for such purposes which satisfies both the need for a limber structure for good range of motion and the stiffness required for good fatigue life.
Improved electrical connection arrangements are desired.